Traction vehicles (such as, for example, locomotives and other off-highway vehicles (“OHVs”)) may employ electric traction motors for driving wheels of the vehicles. In some of these vehicles, the motors are alternating current (AC) motors whose speed and power are controlled by varying the frequency and current of AC electric power supplied to the motors. Commonly, the electric power is supplied at some point in the vehicle system as direct current power and is thereafter inverted to AC power of controlled frequency and amplitude. The electric power may be derived from an on-board alternator driven by an internal combustion engine or may be obtained from a wayside power source such as a third rail or overhead catenary.
In conventional systems the power is inverted in a solid-state inverter incorporating a plurality of diodes and electronic switching devices. In a locomotive, other large OHV, or transit application, the traction motors may develop more than 1000 horsepower per motor thus requiring very high power handling capability by the associated inverter. This, in turn, requires the use of semiconductor switching devices such as GTOs (gate turn-off thyristors) or IGBTs which are capable of controlling such high power and of dissipating significant heat developed in the semiconductor devices due to internal loss generating characteristics.
The semiconductor devices are typically mounted on heat transfer devices such as heat sinks which aid in transferring heat away from the semiconductor devices and thus preventing thermal failure of the devices. An electrical circuit area in which the semiconductors devices are located may include the various control and timing circuits, including low power semiconductors, used in controlling switching of the power semiconductors.
In an OHV, an inverter drive system for large AC motor applications typically includes an inverter associated with each traction motor. A conventional design for power inverters may include a layered bus bar array which interconnects semiconductor device (e.g., IGBT) modules and several DC link capacitors. In particular, a plurality of DC link capacitors are typically connected to the inverters through an arrangement of bus bars including a horizontal, capacitor bus bar that receives a plurality of DC link capacitors and which is coupled to a vertical, interconnecting bus bar. The vertical, interconnecting bus bar is coupled at a distal end to IGBT modules of the inverters.
Known bus bar designs for high power applications, while generally suitable for what is regarded as ordinary performance, may benefit from modified design. In particular, certain existing designs may be prone to corona discharge in the area where the vertical bus bar of the inverters is coupled to the horizontal bus bar, which can lead to insulation degradation and ultimately short circuits.